1. Field
Aspects of the present disclosure relate generally to wireless communication systems, and, more particularly, to apparatus and methods of uplink transmit power control (ULTPC) rejection threshold optimization in WCDMA for power control algorithm 2 (PCA2).
2. Background
Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the UMTS Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). The UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, currently supports various air interface standards, such as Wideband-Code Division Multiple Access (WCDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). The UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA), which provides higher data transfer speeds and capacity to associated UMTS networks.
In a typical wireless communication environment, RF signal transmissions between a base station (e.g., Node B in UMTS) and user equipment (UE) are subject to degradation, such as path loss, shadow fading and multipath, which typically may be caused by such factors as terrain contours (e.g., mountains, forests), environment (e.g., urban or rural), propagation medium (e.g., dry or moist air), changes in distance between a base station (e.g., Node B) and a mobile UE, and/or the like. Transmit power of the UE is typically controlled by uplink (UL) Transmit Power Control (TPC) commands that are sent from the Node B to the UE through a downlink (DL) channel. For example, when a Node B attempts to maintain a signal-to-interference ratio (SIR) target for received signals from the UE, the Node B sends the ULTPC commands to the UE based on how an estimated SIR of a received signal compares to the SIR target. The UE decodes these ULTPC bits (e.g., where a “−1” represents a “down” or reduce power command, “1” represents an “up” or increase transmit power command, and a “0” represents a “hold” command) and adjusts the transmit power accordingly.
The UE can decode a TPC command using one of two algorithms: Power Control Algorithm 1 (PCA1) or Power Control Algorithm 2 (PCA2) as required by the base station. The main difference between the two algorithms is that in PCA1, a UE decodes ULTPC on a per slot basis, while in PCA2, a UE decodes ULTPC on a five-slot interval (also referred to as a five-slot cycle or five-slot period), such that a bit decision is made for each of the five slots and then an overall ULTPC decision is made based on the bit decision for each of the five slots. Since power adjustment is less frequent under PCA2, e.g., once every five slots versus once every slot, TPC command decoding errors and rejections may have a larger impact on transmit power than under PCA1. Both errors and rejections take longer to recover from under PCA2 than under PCA1. For example, a rejection of an overall ULTPC command (which may be referred to as TPC_cmd) decision delays the power adjustment request from Node B by five additional slots. As such, UL throughput may be adversely affected if too many of the ULTPC bit decisions are inaccurate, e.g., there are errors in decoding too many of the bits during the five-slot interval. Further, low rejection rates of bit decisions, e.g., accepting untrustworthy bit determinations, also may negatively affect UL throughput.
Moreover, in a multi-cell situation, such as a soft handover, PCA2 provides that transmit power may be reduced if a single TPC command from one cell is “−1” or “down.” This may referred to as “or-of-down” processing. However, in order to increase transmit power, TPC commands from more than half (e.g., 50%) of the cells need to be “1” or “up.” In a situation where one cell is relatively untrustworthy (e.g., the cell is weak and is not providing a strong enough signal for the UE to accurately determine its TPC command outside of a given margin of error), and the UE decodes a ULTPC command from that cell as indicating a transmit power decrease (e.g., “−1”), while a second cell that is more trustworthy indicates a transmit power increase (e.g., “1”), PCA2 provides that the overall TPC command should be decoded as “down.” As such, if the trustworthy cell truly needed the power increase, but did not get it due to the PCA2 multi-cell requirement, the UE may miss, or drop, a call resulting in a decrease in user experience.
Thus, improvements in TPC command decoding are desired.